This invention relates to improvements in a seat reclining apparatus for a vehicle which apparatus is arranged to angularly adjustably fix a seat back serving as a backrest to a seat cushion on which a vehicle occupant is seated so as to be sustainable even when an excessive load is applied to the seat back.
A seat reclining apparatus for a vehicle is provided to a vehicle seat to angularly adjustably fix a seat back to a seat cushion, by which a position of the seat back can be angularly adjusted with respect to the seat cushion. A conventional seat reclining apparatus includes, for example, a frame installed to a base plate on the side of the seat cushion, and a lid member installed to an arm plate on the side of the seat back. The frame and the lid member are arranged rotatable to each other. An external gear of a lock tooth installed to the frame is engaged with an internal gear formed at the inner peripheral surface of the lid member so as to restrict the relative rotation between the frame and the lid member, thereby keeping the seat back at a certain angle position to the seat cushion.
In order to fix the lock tooth, the frame is projectingly provided with a projecting shaft section and a projecting guide section located in the vicinity of the internal gear. The lock tooth is formed with a depression-shaped bearing surface to be swingably engaged with the shaft section, and a slide surface coaxial with the bearing surface and slidably contacted with a guide surface of the guide section. Additionally, a cam is disposed at the central part of a space defined by the internal gear in order to bias the lock tooth outwardly so as to engage the external gear with the internal gear.
With the above-arranged seat reclining apparatus, when collision occurred at a rear section of an automotive vehicle, a load is applied in such a direction that the seat back falls rearward and acts on the lock tooth through meshing between the internal gear and the external gear. At this time, the lock tooth is supported by the shaft section and the guide section thereby restricting rotation of the lid member relative to the frame, so that the seat back never rotationally falls or inclines rearward.
Further, in conventional techniques, a seatbelt anchor for supporting a force applied to a seatbelt is a center pillar; however, in recent years, vehicles in which the seatbelt anchor is changed from the center pillar to the seat back are increasing. When collision occurs at a front section of such a vehicle, an inertial force due to the vehicle occupant's weight is applied to the seat back in a direction to fall forward, so that the seat back receive a higher load than that in the conventional techniques. Therefore, it is required for the seat reclining apparatus for the vehicle to sustain a significantly high load as compared with that in the conventional techniques.
A seat reclining apparatus to meet the above requirement is disclosed in Japanese Patent Provisional Publication No. 2002-345587, in which the guide section is arranged to be lower than the shaft section in strength in order to decrease occurrence of a bending stress which acts to bend the lock tooth at a portion in the vicinity of a bearing portion. This is intended to prevent breakage of the lock tooth so as to stabilize the strength. In this structure, a clearance is formed between a contact face of the lock tooth and a backup surface of the guide section, so that the contact face cannot be brought into contact with the backup surface when a load is applied in such a direction that the seat back falls forward. As the contact face is not brought into contact with the backup surface, a reactive force from the backup surface never acts on the lock tooth, and therefore the lock tooth does not receive the bending stress thereby being prevented from its breakage.